The selective occlusion of blood vessels in a patient is a part of many modern therapeutic treatments, including the control of internal bleeding, the occlusion of blood supply to tumors, the isolation of diseased body organs prior to removal, the relief of blood pressure in an aneurysm, and the like. While such procedures rely generally on the blockage of arteries, the selective occlusion of veins is also useful in procedures, such as veiniotomy.
The occlusion of blood vessels can be achieved using a variety of specific techniques. For example, chemical occlusion of blood vessels is typically accomplished by introduction of a non-physiological solution into the vessel lumen. The solution is selected to destroy the endothelial wall and injure the underlying tissue, causing edema, fibrin deposition, and eventually fibrosis of the lumen. In addition to the use of such chemical agents, e.g., ethanol, tetradecyl sulfate, and hypertonic saline, heat can also be applied to induce fibrosis of the lumen.
Laser occlusion of blood vessels can be accomplished by introducing the end of a laser fiber within the blood vessel, and transmitting laser energy from the end of the fiber into the endothelial wall of the vessel. For example, Diomed, Inc., located in Andover, Mass., markets a laser-based varicose vein treatment system under the trademark EVLT™ (EndoVenous Laser Treatment).
Radio frequency (RF) occlusion of blood vessels can be accomplished by introducing one or more electrodes into contact with the endothelial of the blood vessel, and conveying RF energy to the electrodes. Exemplary RF devices are disclosed in U.S. Pat. No. 6,077,261, entitled “Device For Permanent Vessel Occlusion,” and U.S. Pat. No. 6,165,172, entitled “Expandable Vein Ligator Catheter and Method of Use.”
The various RF ablation devices disclosed in U.S. Pat. No. 6,077,261 utilize mechanical endoluminal devices that collapse the vessel wall to bring opposing portions of the endothelial wall of the blood vessel partially or completely together. RF energy is then applied to one or more electrodes within the occlusion region between the opposed wall portions to injure or destroy the endothelial cells and underlying tissue in the occlusion region, and initiating a process of thrombosis and fibrosis, which will result in relatively rapid vessel occlusion. Mechanical closure of the endothelial wall slows or stops the flow of blood, greatly enhancing the rate of thermal transfer, which in turn enhances the rate of fibrosis and thrombosis. The RF ablation devices disclosed in U.S. Pat. No. 6,165,172 utilizes a plurality of spoon-shaped electrodes that are circumferentially disposed around the endothelial vessel wall when deployed to provide a uniform distribution of energy and more predictable and efficient occlusion of the vessel. The control system is programmed to maintain the endothelial wall of the blood vessel at a constant temperature, e.g., 85° C., to ensure cross-sectional shrinkage of the blood vessel. A balloon can be used to occlude the blood flow. A commercial embodiment of this type of system is marketed by VNUS Medical Technologies, Inc. under the trademark Closure®.
The above-described vessel occlusion systems allow for the pullback of the relevant ablation device within a sheath as the vessel closes, thereby producing a longitudinal occlusion, which is stronger and less susceptible to recanalization than an acute point occlusion. Venous ablation methods are prone to complications due to technique requirements. Such complications include, but are not limited to incomplete vessel closure, numbness, skin burns, and infection. The major causes of these complications are related to the pullback rate and determining if the vessel is closed. Thus, the ablation device is preferably pulled back at a speed that assures vessel closure.
For example, if the pullback speed of the RF electrodes in the Closure® vessel occlusion system is too rapid, the RF generator will be driven towards the maximum wattage. If this occurs, thermal penetration to the high-collagen-content adventitia can become compromised, resulting in endothelial searing without optimal vein-wall contraction. Slow pull back in the range of 2.5 to 3.5 cm/min, and a thorough post-treatment ultrasound assessment of the entire treated vessel, combined with occasional retreatment of incompletely contracted segments of the vessel should greatly diminish the incidence of early treatment failures. The laser in the EVLT™ should have a slow pull back in the range of 2 to 3 mm/second. Constant compression of the vessel is required to minimize the distance from the laser fiber to the endothelial vessel wall to assure completion ablation/closure of the vessel.
In both the Closure® and EVLT™ venous ablation systems, the physician must pullback the ablation devices manually, and thus, improper pullback can cause incomplete vessel closure or surrounding tissue damage.
Thus, there is a need for an improved venous ablation system and method that assures, or at least maximizes the chance, that vessel closure will be achieved.